The present invention relates to a print head mechanism which is utilized in a high speed printer. More specifically, the present invention relates to a print head mechanism which facilitates easy replacement of the print head and provides for secure positioning of the print head in its operating position.
High speed printers typically utilize a wire matrix print head to perform actual printing function. One typical print head is shown in U.S. Pat. No. 4,051,941 to Hebert, and another is shown in U.S. Patent application Ser. No. 805,706 to Wolf and Slade, filed June 13, 1977 and assigned to Dataproducts Corporation, the same assignee as the present application, the disclosures of which are herein incorporated by reference. In such systems, a plurality of wire stylii are forced against an inked ribbn by means of electromagnetic actuations, thereby imprinting a matrix of minute dots on a printing medium. The symbol which is printed is determined by what stylii of the matrix are forced against the ribbon. The print head is mounted on a shuttle mechanism which traverses the printing medium at a high rate of speed. Because of its rapid rate of operation and wear on the stylii, the print head has a relatively short life when compared to the remainder of the high speed printer, and thus requires periodic replacement. This need for replacement causes two problems to arise. The initial problem is that of ease of replacement. Secondly, and more important, is the fact that the print head must be accurately aligned in the shuttle in order to function properly. The print head must be designed to allow alignment when it is initially mounted, and it must keep this alignment over the period of time for which it is to be used (if periodic adjustment is to be avoided).
With the mounting techniques currently used, quite frequently special tools are required to mount the print head onto the moveable carriage shuttle. In addition, after the print head has been mounted and operation of the printer begun, subsequent adjustments are often needd to properly align the newly installed print head. This is not only expensive, but requires an undue amount of time for the printer operator.
In U.S. Pat. No. 3,921,780 to Gentzlinger and Mailer, a mounting assembly for a print head is set out that does away with need for special tooling, (i.e. a screwdriver may be used). This mounting assembly invloves the use of a circular mounting plate and a ratcheted knob or locking element. It requires that the print head have two accurately aligned mounting studs and one mounting screw. The need for special tools is eliminated, but the assembly still requires that the operator align the print head studs and screw with the corresponding openings in both the carriage and the circular mounting clamp. The mounting clamp must then be rotated and the ratcheted knob threaded on to the mounting screw. Thus, this mounting assembly still tends to be somewhat time consuming. More importantly, though, is the fact that the print head housing, which is normally fabricated from plastic so as to provide a relatively light weight assembly, must be fabricated to include integrally mounted metal studs and a screw. This not only raises the cost of fabricating the print head housing, but also adds undesirable weight to the print head.
The present invention is designed to provide a simple and effective means for mounting and securing a print head to the shuttle of a carriage. The print head includes a cylindrical actuator housing and a tapering guide section or wire guide housing which is attached to the cylindrical actuator housing. A pair of wedge-shaped locking fins are molded on oposite side of the guide section, and a pair of alignment bosses are molded on the guide section a spaced distance from the locking fins. The shuttle includes a generally upright member which includes an opening through which the guide section is inserted. The opening includes a pair of slots which are designed to mate with the the molded bosses so as to rotationally align the print head in the proper operating position. A releasable retaining assembly is mounted on the shuttle and includes a pair of locking members adapted for clamping engagement with the locking fins. Bias spring means are located within the retaining assembly for urging the locking members into clamping engagement with the locking fins. The force exerted by the spring bias means via the locking members and the locking fins urges the cylindrical head section into tight abutting relationship with the upright member of the shuttle. Insertion and removal is thus accomplished quickly and easily simply by releasing the retaining assembly, pulling the print head back until the bosses are free from the slots in the shuttle, and then lifting the print head up through the opening in the shuttle. The bosses serve to properly align the print head in the shuttle and the locking fins serve to hold the print head securely to the shuttle during operation of the printer.
It is therefore a general object of the present invention to provide a mounting assembly whereby a print head is firmly and easily affixed to the printer shuttle without the need of special tools.
It is another object to provide a mounting assembly that requires only the initial positioning of the print head with no subsequent alignment adjustments being required.
It is a further object of the invention to provide a print head wherein all necessary alignment or securing devices may be integrally molded as part of the print head.